1. Field of the Invention
The present invention relates to a method and an apparatus for measuring an eccentricity of the vertex of an aspherical surface of an aspherical lens (at least one lens surface of which is formed as an aspherical surface) with respect to the radial center of the aspherical lens, an eccentricity of the curvature center of the other lens surface thereof (an aspherical lens surface or a spherical lens surface), and the degree of deviation of the other lens surface. The present invention also relates to a method and an apparatus for centering and edging an optical lens (at least one lens surface of which is formed as an aspherical surface) while reducing an eccentricity of the vertex of an aspherical surface of the optical lens with respect to the true aspherical-surface axis of the aspherical lens surface of the optical lens even if the optical lens is a tilted aspherical lens.
2. Description of the Related Art
In an aspherical lens, at least one lens surface of which is formed as an aspherical surface, if an eccentricity of the vertex of the aspherical surface (the point of intersection of the aspherical surface with the aspherical-surface axis thereof that linearly extends to trace the respective curvature centers of the aspherical surface at different points thereon) with respect to the radial center of the aspherical lens can be measured, i.e., if the radial distance of the vertex of the aspherical surface from the radial center of the aspherical lens can be measured, the influence of the eccentricity of the vertex of the aspherical surface with respect to the radial center of the aspherical lens on the optical performance of the aspherical lens can be observed by studying the correlation between the eccentricity and the optical performance of the aspherical lens.
However, in the prior art, uncertainty about the reference for measurement of the eccentricity remains because the aspherical-surface axis of the aspherical surface is conventionally determined from the curvature center of a given portion of the aspherical surface. For instance, in an aspherical lens having an aspherical surface, the curvature center of which varies greatly between inner and outer portions of the aspherical surface, no conventional methods or apparatuses for precisely measuring an eccentricity of the vertex of the aspherical surface with respect to the radial center of the aspherical lens are known in the art.
In an aspherical lens, at least one lens surface of which is formed as an aspherical surface, if the degree of deviation of the aspherical surface from a spherical surface is large, it is often the case that the degree of eccentricity of the vertex of the aspherical surface with respect to the radial center of the aspherical lens deteriorates the aberration of the whole lens system, more than the degree of tilting of the aspherical-surface axis of the aspherical surface with respect to the radial center of the aspherical lens does, in the case where the aspherical lens is installed in the vicinity of a diaphragm in the lens system.
However, uncertainty about the reference for machining the aspherical lens remains because the aspherical-surface axis of the aspherical surface is conventionally determined from the center of curvature of a given part of the aspherical surface. For instance, in an aspherical lens having an aspherical surface, the curvature center of which varies greatly between inner and outer portions of the aspherical surface, no methods or apparatuses for centering and edging the aspherical lens, so that an eccentricity of the vertex of the aspherical surface with respect to the radial center of the aspherical lens becomes small, are known in the art.
Moreover, no methods or apparatuses for centering and edging a tilted aspherical lens so that an eccentricity of the vertex of the aspherical surface with respect to the radial center of the aspherical lens becomes small are known in the art. Note that a tilted aspherical lens refers to an aspherical lens designed so that the curvature center of the spherical surface on the other lens surface is not positioned on the aspherical-surface axis of the aspherical surface if one and the other lens surfaces of the aspherical lens are a spherical surface and an aspherical surface, respectively, or the optical axes of both lens surfaces are inclined to each other if each of one and the other lens surfaces of the aspherical lens is formed as an aspherical surface.